Furnace skids and beams

ABSTRACT

A skid or beam for a slab reheating furnace has a hollow fluid cooled pipe on which are supported a number of elongate slab engaging rail portions. The rail portions are alternately offset from the vertical symmetrical plane of the pipe. The pipe is shaped to minimize shielding of the slab from the radiant heat of the furnace and may have a triangular cross section or a rectangular cross section. The offsetting of the rail portions reduces skid marks caused by conduction from the hot slab to the cooled pipe. The rail portions are of inverted channel section.

United States Patent Laws [ 1 Feb. 15,1972

[54] FURNACE SKIDS AND BEAMS [72] inventor: William Robert Laws, Worcester Park,

England [73] Assignee: The British Iron and Steel Research Association, London, England [22] Filed: June 17,1970

[2i] Appl.No.: 46,863

[30] Foreign Application Priority Data July 16, 1969 Great Britain ..35,859/69 [56] References Cited UNITED STATES PATENTS 3,552,729 1/1971 Hepp et al ..263/6 B 3,304,070 2/1967 Jones ..263/6B 3,337,199 8/1967 Kirkpatrick ..263/6 B X FOREIGN PATENTS OR APPLICATIONS 969,079 4/ 1958 Germany .263/6 B l,3l4,954 12/ I962 France ..263/6 B Primary Examiner-Charles J. Myhrc Attorney-Bacon and Thomas [57 1 ABSTRACT A skid or beam for a slab reheating furnace has a hollow fluid cooled pipe on which are supported a number of elongate slab engaging rail portions. The rail portions are alternately offset from the vertical symmetrical plane of the pipe. The pipe is shaped to minimize shielding of the slab from the radiant heat of the furnace and may have a triangular cross section or a rectangular cross section. The offsetting of the rail portions reduces skid marks caused by conduction from the hot slab to the cooled pipe. The rail portions are of inverted channel section.

12 Claims, 4 Drawing Figures PAIENTEDFEB 15 I972 SHEET 2 0F 3 INVENTOI? WILLIAM R0552? Laws H 7'TORNEY5 FURNACE SKIDS AND BEAMS This invention relates to skids and beams for furnaces such as slab reheating pusher furnaces and walking beam furnaces in which the slabs or billets are heated both from above and below.

It is an object of the invention to provide a skid or beam which minimizes the formation of cooler regions in the slabs or billets known as skid marks.

According to the present invention there is provided a skid or beam for a furnace including a hollow pipe adapted to allow a cooling fluid to be passed therethrough, and slab engaging means supported on the upper portion of the pipe characterized in that the slab engaging means consists of a plurality of elongate rail portions disposed along the length of the pipe and alternately offset from the vertical center plane of the pipe.

It has been found that skid marks are partly formed by the skid shielding the slab from the heat radiated from under the slab, and partly by reradiation and conduction from the slab to the rail and hence to the pipe which is cooled to maintain its mechanical strength. By offsetting the rail portions, the same point on the slab does not always contact the skid. Proposals have previously been made to offset the whole of one portion of a skid with respect to the next portion, but this has the disadvantage that the mechanical strength of the skid is reduced because it is not continuous and it creates problems in assembling the skid in the furnace. By contrast the skid according to the present invention can have a continuous pipe running the whole length of the furnace.

Offsetting of the rail portions with respect to the pipe is particularly advantageous when the pipe is shaped to minimize shielding of the slab or billet because then reradiation and conduction are more significant as a factor in forming the skid mark. Hitherto it has not been realized that the small amount of offsetting of the rail portions that can be achieved with respect to the pipe can make any appreciable difference to the skid marks.

To minimize shielding while maintaining sufficient mechanical strength the maximum height of the pipe preferably exceeds its maximum width. The pipe may have a generally rectangular cross section of greater height than its width, or the pipe may have a generally triangular cross sectlon.

The rail portions are preferably of inverted channel section with two outer limbs extending downwardly from an upper part, the lower ends of the outer limbs being secured to the pipe. Thus the area of the rail portions contacting the pipe is substantially less than the area contacting the slab so as to minimize conduction from the rail portions to the pipe.

In the accompanying drawings:

FIG. 1 is a cross section through a pusher furnace with skids embodying the invention,

FIG. 2 is a perspective view of part of one skid embodying the invention,

FIG. 3 is a cross section through the skid of FIG. 2, and

FIG. 4 is a cross section through another skid embodying the invention.

FIG. 1 shows a slab reheating pusher furnace 1 with six skids 2 each supported on a supporting structure 3. A steel slab 4 is shown supported on the skids 2. There are burners 5 above and below the skids 2 and heat is radiated to the slabs 3 from the burner flames and from the walls 6 of the furnace 1.

FIGS. 2 and 3 show a skid 2 in more detail. The skid 2 includes a hollow skid pipe 7 arranged to allow a cooling fluid to be passed therethrough, and slab engaging skid rail portions 8 supported on the upper portion of the pipe 7. The pipe 7 is symmetrical about its vertical center plane and is of generally triangular cross section with generally flat surfaces 9 converging towards the rail portions 8 over a major portion of the height ofthe pipe 7.

The rail portions 8 are of channel section with two outer limbs 10, 11 supported on the pipe 7 so that a space 12 is enclosed by the rail portions 8 and the pipe 7. The limbs 10, ll

extend down from an upper part 13 of the rail portions 8. The width of the limbs 10, 11 is such that the area of the rail 4 that contacts the pipe 7 is substantially less than the upper surface of the upper part 13 of the rail portions that contact the slab. The limbs 10 are longer than the limbs 11 so that the upper parts 13 of the rail portions 8 are horizontal and level with one another. The rail portions 8 are alternately ofiset from the vertical center plane of the pipe 7. The length of the portions 8 is chosen so that slabs passing through the furnace will engage at least two adjacent portions to ensure that the pipe 7 will not be subjected to torsional stress about its longitudinal axis. Slabs are usually of the order of 1 meter wide, and accordingly the length of each rail portion 8 is less than 1 meter. There is a small gap between rail portions 8 to allow for thermal expansion of the rail portions 8.

The lower ends of the limbs 10, 11 are welded to the pipe 7 with weld material 14.

A layer of thermal insulating material 15 surrounds the pipe 7 for insulating the pipe. The material 15 is formed in pieces, and as seen in cross section, two pieces surround the pipe 7. Reinforcing mesh 16 is welded to the pipe 7 at 17 to secure the pieces in place. Refractory filling material 18 is used to fill the gaps between the top of the material 15 and the rail portions 8. The upper surfaces 19 of the insulating material 15 are substantially flat and converge towards the rail portions 8.

Stress relieving discontinuities 20 are formed in the upper part 13 of each rail portion 8 and are spaced along the length of the rail portions 8. The discontinuities 20 consist of grooves extending across the upper surface of the rail portions 8 and down at least part of the limbs 10 and 11. The grooves 20 terminate in holes 21 passing right through the limbs 10 and 11. The rail portions 8 are made of 50 to 51 percent cobalt steel alloy which is a wear resisting material which can be operated for long periods at high temperatures such as l,000 C. It is found that the temperature difference between the top and bottom of each rail portion 8 causes stresses in the rail portion, but the provision of the grooves 20 allows the rails to crack at these predetermined points along the length of the rail and this prevents the rail from curving and breaking the weld between the rail portions 8 and the pipe 7. The holes 21 serve to limit the cracks.

The converging surfaces 19 of the insulated skid produce less shielding of the slab from heat radiated from the bottom walls 6 of the furnace than do conventional circular pipes.

' The alternately offset rail portions 8 ensure that the same point on the slab does not always contact the skid so that skid marks caused by shielding, reradiation and conduction are not concentrated in the slab. The combination of the skid shaped to minimize shielding and the offset rail portions minimizes skid marks.

The skid rail shown in FIG. 4 consists of a pipe 30 of generally rectangular cross section with a maximum height greater than its maximum width. Channel-shaped rail portions 31 are welded to the top surface of the pipe 30 and are offset as in the skids shown in FIGS. 2 and 3. Insulating material 32 is secured to the pipe 30 in generally the same way as in FIGS. 2 and 3.

The rectangular pipe 30 provides a convenient surface for supporting symmetrical rails 31. A pipe of rectangular cross section which is taller than its width provides less shielding than a pipe of square cross section and provides greater stiffness against vertical deflection.

' After a slab or billet emerges from a reheating furnace it is rolled, and for the rolling to be satisfactory the whole of the slab or billet must be above a certain temperature. The coolest parts of the slab, namely the skid marks, have to be raised above this certain temperature and therefore the rest of the slab has to be raised to a higher temperature than is necessary for satisfactory rolling. By diminishing the skid marks by use of skids according to the invention it is thus possible to lower the overall furnace temperature which results in a saving in fuel and an increased life for the refractory materials lining the furnace. Alternatively greater throughput can be achieved if the furnace is operated at maximum temperature.

lclaim:

l. A skid or beam for a furnace including a hollow pipe adapted to allow a cooling fluid to be passed therethrough, and slab engaging means supported on the upper portionof the pipe characterized in that the slab engaging means consists of a plurality of elongate rail portions disposed along the length of the pipe and alternately offset from the vertical center plane of the pipe, alternate rail portions being spaced apart longitudinally.

2. A skid or beam as claimed in claim 1 in which the length of each rail portion is less than I meter.

3. A skid or beam as claimed in claim 1 in which the rail portions are of inverted channel section with two outer limbs extending downwardly from an upper part, the lower ends of the outer limbs being secured to the pipe.

4. A skid or beam as claimed in claim 3 in which the rail portions are made of 50 to 51 percent cobalt steel alloy.

5. A skid or beam as claimed in claim 1 in which the maximum height of the pipe exceeds its maximum width.

6. A skid or beam as claimed in claim 1 in which the pipe has a generally rectangular cross section.

7. A skid or beam as claimed in claim I in which the pipe has a generally triangular cross section.

8. A skid or beam as claimed in claim 1 including a layer of thermal insulating material surrounding the pipe.

9. A furnace having heating means disposed both above and below skids or beams for supporting slabs to be heated, each skid or beam including a hollow pipe adapted to allow a cooling fluid to be passed therethrough and slab engaging means supported on the upper portion of the pipe, characterized in that the slab engaging means consists of a plurality of elongate rail portions disposed along the length of the pipe and altemately offset from the vertical central plane of the pipe, al-

, ternate rail portions being spaced apart longitudinally.

10. A furnace as claimed in claim 9 in which the rail portions are of inverted channel sections with two outer limbs extending downwardly from an upper part, the lower ends of the outer limbs being secured to the pipe.

11. A skid or beam for a furnace including a hollow pipe adapted to allow a cooling fluid to be passed therethrough, and slab engaging means supported on the upper portion o the pipe characterized in that the slab engaging means consists of a plurality of elongate rail portions disposed along the length of the pipe and alternately offset from the vertical center plane of the pipe, alternate rail portions being spaces apart longitudinally, the longitudinal spacing of the rail portions on one side of said vertical center plane being arranged to be substantially equal to the length of the rail portions on the other side of said vertical center plane.

12. A skid or beam for a furnace including a hollow pipe adapted to allow a cooling fluid to be passed therethrough, and slab engaging means supported on the upper portion of the pipe characterized in that the slab engaging means consists of a plurality of elongate rail portions disposed along the length of the pipe and alternately ofl'set from the vertical center plane of the pipe, alternate rail portions being spaced apart longitudinally, the spacing of the rail portions on one side of said vertical center plane being substantiallyequal to the length of the rail portions on the other side of said vertical center plane, the length of the rail portions on either side of said vertical center plane being less than the length of a slab to be heated thereon whereby the slab will engage at least two adjacent offset rail portions. 

1. A skid or beam for a furnace including a hollow pipe adapted to allow a cooling fluid to be passed therethrough, and slab engaging means supported on the upper portion of the pipe characterized in that the slab engaging means consists of a plurality of elongate rail portions disposed along the length of the pipe and alternately offset from the vertical center plane of the pipe, alternate rail portions being spaced apart longitudinally.
 2. A skid or beam as claimed in claim 1 in which the length of each rail portion is less than 1 meter.
 3. A skid or beam as claimed in claim 1 in which the rail portions are of inverted channel section with two outer limbs extending downwardly from an upper part, the lower ends of the outer limbs being secured to the pipe.
 4. A skid or beam as claimed in claim 3 in which the rail portions are made of 50 to 51 percent cobalt steel alloy.
 5. A skid or beam as claimed in claim 1 in which the maximum height of the pipe exceeds its maximum width.
 6. A skid or beam as claimed in claim 1 in which the pipe has a generally rectangular cross section.
 7. A skid or beam as claimed in claim 1 in which the pipe has a generally triangular cross section.
 8. A skid or beam as claimed in claim 1 including a layer of thermal insulating material surrounding the pipe.
 9. A furnace having heating means disposed both above and below skids or beams for supporting slabs to be heated, each skid or beam including a hollow pipe adapted to allow a cooling fluid to be passed therethrough and slab engaging means supported on the upper portion of the pipe, characterized in that the slab engaging means consists of a plurality of elongate rail portions disposed along the length of the pipe and alternately offset from the vertical central plane of the pipe, alternate rail portions being spaced apart longitudinally.
 10. A furnace as claimed in claim 9 in which the rail portions are of inverted channel sections with two outer limbs extending downwardly from an upper part, the lower ends of the outer limbs being secured to the pipe.
 11. A skid or beam for a furnace including a hollow pipe adapted to allow a cooling fluid to be passed therethrough, and slab engaging means supported on the upper portion of the pipe characterized in that the slab engaging means consists of a plurality of elongate rail portions disposed along the length of the pipe and alternately offset from the vertical center plane of the pipe, alternate rail portions being spaces apart longitudinally, the longitudinal spacing of the rail portions on one side of said vertical center plane being arranged to be substantially equal to the length of the rail portions on the other side of said vertical center plane.
 12. A skid or beam for a furnace including a hollow pipe adapted to allow a cooling fluid to be passed therethrough, and slab engaging means supported on the upper portion of the pipe characterized in that the slab engaging means consists of a plurality of elongate rail portions disposed along the length of the pipe and alternately offset from the vertical center plane of the pipe, alternate rail portions being spaced apart longitudinally, the spacing of the rail portions on one side of said vertical center plane being substantially equal to the length of the rail portions on the other side of said vertical center plane, the length of the rail portions on either side of said vertical center plane being less than the length of a slab to be heated thereon whereby the slab will engage at least two adjacent offset rail portions. 